Method and apparatus for separating a carbon dioxide-rich gas

Abstract

In a purification method, a carbon dioxide-rich gas is cooled in a first brazed aluminum plate-fin heat exchanger, the cooled gas or at least one fluid derived from the cooled gas is sent to a purification step comprising a distillation step, the purification step produces a carbon dioxide-rich liquid which is cooled, then expanded, then sent to a second heat exchanger where it is heated by means of a fluid of the method, the exchanger carrying out an indirect heat exchange only between the carbon dioxide-rich liquid and the fluid of the method, the carbon dioxide-rich liquid at least partially vaporizes in the second exchanger and the vaporized gas formed heats up again in the first exchanger to form a carbon dioxide-rich gas.

The invention claimed is: 
     
       1. A method of purifying a carbon dioxide-rich feed gas at a sub-ambient temperature in order to produce a carbon dioxide-rich product stream, the method comprising the steps of:
 i) cooling and partially condensing the carbon dioxide-rich feed gas in a first heat exchanger to form a partially condensed carbon dioxide-rich fluid, wherein the first heat exchanger is of a brazed aluminum plate heat exchanger comprising corrugated layers separated by plates; 
 ii) introducing the partially condensed carbon dioxide-rich fluid to a first phase separator to produce a first gas at a top of the first phase separator and a first liquid at a bottom of the first phase separator; 
 iii) introducing the first gas to a second heat exchanger and condensing said first gas within the second heat exchanger against an expanded carbon dioxide-rich liquid thereby forming a second bottom fluid at a bottom of the second heat exchanger and a second gas at a top of the second heat exchanger, wherein the second heat exchanger is a shell and tube heat exchanger, wherein the second heat exchanger comprises a plurality of tubes disposed within the shell; 
 iv) introducing the second bottom fluid to a second phase separator to produce a third gas at a top of the second phase separator and a third liquid at a bottom of the second phase separator; 
 v) introducing the first liquid from the first phase separator and the third liquid from the second phase separator to a distillation column to produce a head gas at a top of the distillation column and a bottoms liquid at a bottom of the distillation column, wherein the head gas is carbon dioxide-lean as compared to the first liquid, wherein the bottoms liquid is carbon dioxide-rich as compared to the first liquid; 
 vi) subcooling the bottoms liquid without prior expansion to form a subcooled carbon dioxide-rich liquid and then expanding the subcooled carbon dioxide-rich liquid to form the expanded carbon dioxide-rich liquid; 
 vii) vaporizing the expanded carbon dioxide-rich liquid in the second heat exchanger to form the second gas at the top of the second heat exchanger, wherein the second gas is carbon dioxide-rich; 
 viii) warming the second gas in the second heat exchanger and then the first heat exchanger to form the carbon dioxide-rich product stream, 
 ix) warming the third gas from the second phase separator in a third heat exchanger; 
 x) then introducing the third gas to a membrane separator to produce a permeate stream and a non-permeate stream, 
 xi) warming the non-permeate stream in the first heat exchanger; 
 xii) warming the permeate stream in the first heat exchanger prior to using the permeate stream to regenerate an adsorbent bed; 
 xiii) recycling the permeate stream from the adsorbent bed to the carbon dioxide-rich feed gas upstream of the first heat exchanger, 
 wherein the bottoms liquid is subcooled in step vi) in the third heat exchanger. 
 
     
     
       2. The method as claimed in  claim 1 , wherein the first gas from the first phase separator is condensed within the tubes of the second heat exchanger, and the expanded carbon dioxide-rich liquid is vaporized in the shell of the second heat exchanger. 
     
     
       3. The method as claimed in  claim 1 , wherein the first gas from the first phase separator and the expanded carbon dioxide-rich liquid are the only two fluids exchanging heat within the second heat exchanger. 
     
     
       4. The method as claimed in  claim 1 , wherein the head gas from the distillation column is heated in the first heat exchanger. 
     
     
       5. The method as claimed in  claim 1 , wherein the carbon dioxide-rich feed gas comprises an impurity selected from the group consisting of oxygen, nitrogen, argon, nitrogen oxides, carbon monoxide, hydrogen, mercury and combinations thereof. 
     
     
       6. The method as claimed in  claim 1 , wherein the shell of the second heat exchanger is operated at a pressure corresponding with the triple point of carbon dioxide.